In July 2006, Russian dissident Vladimir Bukovsky and former KGB colonel Oleg Gordievsky co-wrote a letter to The Times in London.
A new Russian law empowered President Vladimir Putin to "use his secret services as death squads to eliminate extremists anywhere abroad, including in this country", the letter warned.
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A British inquiry has concluded the murder of ex-Russian spy Alexander Litvinenko in 2006 was "probably" approved by President Vladimir Putin. Courtesy ABC News 24.
"The stage is set for any critic of Putin's regime here ... to have an appointment with a poison-tipped umbrella."
The list of targets was "already compiled", they claimed.
The Times headlined the letter "Licence to Kill".
Four months later Bukovsky's close friend Alexander Litvinenko was dead, the victim of a James Bond-like assassination plot: radioactive poison hidden in an afternoon pot of tea at a stylish Mayfair hotel.
An official inquiry this week concluded it was a deliberate assassination by a pair of Russians, most likely ordered by the Russian secret services, and "probably" pre-approved by Putin himself.
But it may have gone unnoticed, a crime unsolved or even undiscovered, had Litvinenko not hung grimly on to life until a nuclear scientist made an extraordinary discovery.
Litvinenko was born in December 1962 in the Russian city of Voronezh. He went to military college, in the footsteps of his grandfather who fought in the Second World War. He was quickly recruited into the KGB – training in Siberia then posted to Moscow in the late '80s.
He focused on combating organised crime, and became convinced of collusion between officials of the FSB – including Vladimir Putin and Nikolai Patrushev – and the "Tambov" criminal group that smuggled heroin from Afghanistan to western Europe.
In 1998 he held a press conference denouncing the FSB, Russia's Federal Security Service and successor organisation to the KGB (of which Mr Putin was then the director), calling it corrupt, criminalised and a "system from which people needed to be protected".
He was subsequently arrested several times, and finally left Russia in October 2000 with his family. He landed at Heathrow, walked up to the first police officer in the arrivals hall and said: "I am KGB officer and I'm asking for political asylum."
In 2006 the family were naturalised as British citizens. Litvinenko was working as a journalist and adviser on Russian individuals and organisations (and almost certainly working for, or at least advising MI6).
Suddenly, on the night of November 1, 2006, he began vomiting "again and again", his widow said. He was taken to hospital.
He and his family almost immediately suspected poisoning. Baffled doctors said that was unlikely, but two weeks later one noticed the symptoms were a good match for a leukaemia patient who had been zapped with intense radiotherapy. He made a note to radiology: "check radioactive sources of poisoning."
A Geiger counter detected nothing, but on November 21 a hospital pharmacist suggested a radioisotope could have been used to poison Litvinenko. Blood and urine samples were sent to the British Atomic Weapons Establishment, which revealed the presence of polonium-210.
A second test confirmed the result on November 23 – the day Mr Litvinenko, his body wracked by toxins and cell death, died after his third cardiac arrest.
An autopsy revealed he had twice swallowed polonium-210, the earlier dose 100 times smaller than the latter, which killed him.
Shocked police –who had never had to deal with such an (apparent) murder before – realised they had a unique investigative tool, if they acted fast. Even invisible quantities of polonium-210 are deadly if ingested, and it quickly fades into the background due to its short radioactive half-life. But while it is active it leaves an indelible trail.
Tracking Litvinenko's movements before his illness, they found heavy polonium-210 contamination in the Pine Bar of the Millennium Hotel in swanky Mayfair – where he had taken tea with two "businessmen".
The men were Andrei Lugovoi and his associate Dmitry Kovtun – former Russian army officers. Lugovoi was a former KGB agent. Kovtun was a childhood friend of Lugovoi, who served with him in the army and was described as a "businessman in the oil and gas industry".
Both are now wanted for Litvinenko's murder.
They had met Litvinenko first on October 16 and 17 in a meeting room in a Japanese restaurant that later tested positive for polonium exposure, as did their London hotel rooms and their plane seats on the flight to Moscow on October 18.
It was a failed assassination attempt, Sir Robert Owen concluded in his inquiry report this week.
A week later Lugovoi flew back to London – leaving a radioactive trail on a car, a photocopier, a sofa and his Sheraton hotel room (the Sheraton readings were the highest in the whole investigation).
Kovtun then joined him in London, having left radioactive traces dotted around Hamburg in the meantime. According to an unnamed German witness, there he was overheard saying: "Litvinenko was a traitor, there is blood on his hands." Kovtun asked for the contact of a cook working in London, saying, "he had a very expensive poison and needed the cook to administer it to Litvinenko".
"It's meant to set an example," Kovtun said, according to the witness.
In London Lugovoi and Kovtun (among other things) went on a "Big Bus" sightseeing tour of London with Lugovoi's family.
About 4pm on November 1, Litvinenko met the pair in the Pine Bar of the Millennium Hotel, where Kovtun, Lugovoi and Lugovoi's family were staying.
A staff member remembered the three men. Part of the order was "green tea with lemon and honey", brought to the table in a white porcelain pot.
Later, Litvinenko recalled "it was green tea with no sugar and it was already cold ... I didn't like it ... maybe in total I swallowed three or four times".
Police later found polonium contamination in the hotel room used by Lugovoi, and much higher readings in the room used by Kovtun – the highest under the bathroom plughole.
They also found "primary contamination" on the Pine Bar table used by the three men, on the chairs, and "extremely high" readings on just one of the bar's white teapots.
The highest readings were on the inside of the spout.
Given the amount of polonium possessed and used by the assassins, it "strongly indicated" the involvement of a state, Sir Robert said.
"Ordinary criminals might have been expected to use a straightforward, less sophisticated means of killing ... the polonium-210 used to kill Mr Litvinenko must have come from a reactor and such reactors are in general under state control."
Sir Robert said this amounted to "strong circumstantial evidence" of Russian state responsibility for the murder.
But, frustratingly, the public report released on Thursday didn't set out the key evidence relied on by Sir Robert in pinning the assassination on the FSB.
That evidence was delivered in closed court – reportedly in testimony and documents provided by agents from Western intelligence services.
It is that evidence, Sir Robert said, that made it a "strong probability" that Lugovoi poisoned Litvinenko under FSB direction.
So – how high up did it go? Litvinenko himself had no doubt.
On his deathbed he signed a statement accusing the Russian President.
"As I lie here I can distinctly hear the beating of wings of the angel of death," he wrote. "You have shown yourself to be as barbaric and ruthless as your most hostile critics have claimed ... you may succeed in silencing one man but the howl of protest from around the world will reverberate, Mr Putin, in your ears for the rest of your life."
Sir Robert said Litvinenko's shocking claim – denied by Russia, and doubted even by many in Britain (Home Secretary Theresa May initially refused to hold an inquiry, though her hand was forced when Litvinenko's widow won the support of the High Court) was "probably" true.
Sir Robert said many organisations and individuals within the Russian state had powerful motives to take action against Mr Litvinenko – "including killing him".
"Mr Litvinenko was, as a result of his actions both before and after leaving Russia, regarded as having betrayed the FSB. Moreover, according to Mr Lugovoi, the FSB had received information that Mr Litvinenko was working for British intelligence. Mr Litvinenko was an associate of leading opponents of the Putin regime, and he had repeatedly targeted President Putin himself with highly personal public criticism."
It's likely this is a reference to an inflammatory article Litvinenko wrote in July 2006 for the fringe news site "Information Liberation", titled "The Kremlin Paedophile".
Yuri Shvets told the inquiry "I strongly believe that [the killing] couldn't be done without Vladimir Putin's knowledge, because of one of the key traditions of the KGB ... KGB rule No. 1 [is] cover your back, and covering your back is to get approval from your superior."
And Russian dissident Alex Goldfarb, who helped Litvinenko escape Russia, said it was an "inevitable conclusion" that "no one else than Mr Putin" approved the killing – "traditionally this sort of active measures from Soviet times are authorised at the highest political level".
In his report, Sir Robert said these men could not claim to be impartial observers. He relied instead on Robert Service, a professor of Russian history at Oxford University.
Professor Service said it was "inconceivable" that [then FSB chief] Mr Patrushev didn't know about the operation.
He said Mr Putin "endorsed" the FSB's operations and was more hands-on than a mere "general sanction" of its work. However, Mr Putin's specific knowledge and approval of the Litvinenko operation (and others) was a "known unknown".
Sir Robert went further, however. Despite Professor Service's reservations, "drawing on the logic of his analysis relating to other matters ... Mr Patrushev probably would have told President Putin about such an operation".
The "logic" is footnoted to a paragraph in Professor Service's statement to the inquiry.
It says: "A politician with Putin's past career in the intelligence agencies and his sustained interest in security policy" would probably have prior alerts about assassination attempts. But it adds the analysis is "inconclusive".
Certainly it's true that Putin enjoys taking a keen interest in security operations. In the officially sanctioned documentary Crimea: The Way Home on Russia's annexation of Crimea, Mr Putin in a long interview proudly reveals that he invited the heads of his security services to the Kremlin, and personally supervised the extraction of deposed president Viktor Yanukovych from eastern Ukraine – staying up the whole night to micromanage the operation.
Sir Robert didn't just build the case against Russia. He judicially dismissed arguments on both sides, and was wary of the testimony of Litvinenko's former colleagues and friends – and those with an axe to grind against the Kremlin.
He rejected a "chemical fingerprint" theory that definitively traced the polonium to afactory in Sarov, Russia, though it "unquestionably" could have come from there.
He also cast heavy doubt on evidence from a "Mr Potemkin" that the polonium came from an August 2006 shipment to the FSB in Moscow.
He also dismissed an incident cited in Lugovoi's defence, that he encouraged Litvinenko to shake his eight-year-old son's hand at the end of the meeting at the hotel. Sir Robert concluded that Lugovoi knew he had administered a poison, but probably didn't know its nature.
He also ruled out claims of suicide or accident, and dismissed a polygraph test undertaken by Lugovoi in 2012 as "seriously flawed" in its technique and results.
Lugovoi, now a deputy in the State Duma and awarded an honour for "services to the fatherland", said the report had "debunked the myth of the impartiality of British justice" and the charges against him were "absurd".
Moscow's ambassador to Britain Alexander Yakovenko accused Britain of "blatant provocation" in making the link to the Kremlin and dismissed the report as "a whitewash for British special services' institutional incompetence" and an "attempt to put additional pressure on Russia in connection with existing differences over a number of international issues".
It would "still further poison the atmosphere of our bilateral relations", a spokesman for Mr Putin said.
But the British government, in turn, blew sound and fury that amounted to little.
Home Secretary Theresa May told Parliament the killing was "a blatant and unacceptable breach of the most fundamental tenets of international law and of civilised behaviour".
She said she had received one recommendation from Sir Robert, which she could not reveal (almost certainly because it related to Britain's secret services).
But she said she had written to her counterparts in EU, NATO and Five Eyes countries (the latter includes Australia), "drawing their attention to both the report and the need to take steps to prevent such a murder being committed on their streets".
In terms of direct action, she announced that Lugovoi and Kovtun – already the target of international arrest warrants – would be subject to new "asset freezes" imposed by the Treasury.
And Prime Minister David Cameron said Britain had "always believed" that it was a state-sponsored killing but "we at some level have to go on having some sort of relationship with [Russia]".
Polonium-210 has a half-life of just 138 days – meaning that, by now, it is 17 million times less radioactive as the day Litvinenko was poisoned.
His body lies in a (now needlessly) lead-lined coffin in a corner of the beautiful, tree-lined Highgate cemetery in North London, in a section accessible only on official tours. His neighbours are mostly not particularly famous Victorian-era architects and north London residents.
"It's an area people often choose because it's more private," the cemetery chief executive said.
Elsewhere in the cemetery lie such famous corpses as Karl Marx, Sidney Nolan, Malcolm McLaren and Douglas Adams.
But few lie as restless as Litvinenko.
Polonium-210 – what is it?
- Marie and Pierre Curie discovered this rare element in 1897
- It's a silver-coloured isotope of polonium found in uranium ore
- It has some industrial uses, eg, for example in commercial devices that remove static
- About 100 grams of polonium-210 is manufactured every year worldwide, by bombarding the element bismuth-209 with neutrons inside a nuclear reactor
- It is highly radioactive – and so extremely poisonous. The "safe" amount of polonium-210 to ingest is just 7 picograms (there are a thousand billion picograms in a gram)
- A microgram (one millionth of a gram) of polonium-210, the size of a barely-visible speck of dust, would deliver a fatal dose of radiation if swallowed
- Once ingested it sits in the body for a month, wreaking havoc by creating poisonous radicals from any molecule it encounters, and killing or damaging the body's cells
- Litvinenko is the only known polonium fatality.
Source: Royal Society of Chemistry
Poison, murder and plots:
- Anna Politkovskaya, a Russian journalist for the Novaya Gazeta newspaper (and close friend of Litvinenko), was murdered by gunmen outside her Moscow apartment on October 7, 2006. She was a prominent critic of Vladimir Putin.
- In September 2004 Viktor Yushchenko, anti-Moscow candidate for the Ukraine presidency, was horrifically disfigured by a poison later identified as a dioxin. Shortly before becoming ill, he had dinner with the chairman of the Ukrainian Security Service and his deputy. The poisoning was attributed to Russian agents.
- Sergei Yushenkov, a co-founder of the oppositionist Liberal Russia party in 2002, was shot dead in a street in Moscow in April 2003. Another founder of the party, Vladimir Golovlev, was shot and killed in Moscow the same year.
- In February 2004 Chechen vice-president Zelimkhan Yandarbiyev was blown up as he left a mosque in Qatar with his son. He was a strong critic of the Putin administration. Three agents of Russian military intelligence were later arrested and accused of planting the bomb.
- In 2003, Russian politician Yury Shchekochikhin died of apparent poisoning, after many years campaigning against corruption in Russia and FSB malpractice.
- In 1978, Bulgarian dissident Georgi Markov was assassinated on a London street when an agent, said to be assisted by the KGB, fired a pellet of poisonous ricin into his leg using the tip of an umbrella.